The antimalarial drug artemisinin and a number of its derivatives were tested for their effects on proliferation of undifferentiated neuroblastoma Nb2a cells and glioma C6 cells in culture as well as their ability to inhibit neurite outgrowth from Nb2a cells differentiated by removal of serum and addition of dibutyryl cyclic AMP. In the Nb2a and C6 cell cultures, all drugs except desoxyartemisinin significantly inhibited cell proliferation in a dose-related manner with the lowest effective concentration being that of artemisinin at 0.1 microM. Artemether, arteether, artemisinin and dihydroartemisinin also produced a dose-related decrease in the number of neurites/extensions formed by differentiating Nb2a cells, with an effect of dihydroartemisinin at a concentration as low as 1 nM. Desoxyartemisinin had no effect on extension/neurite formation. We propose a potential mechanism for neurotoxicity of artemisinin and its derivatives that involves the endoperoxide bridge which is also known to be necessary for their antimalarial action.